


Window of Opportunity

by cardboardhydrates



Category: Undertale (Video Game)
Genre: Alternate Universe - Underfell, Alternate Universe - Underswap, Blackmail, Bodyswap, Deception, M/M, Underfell Sans, Underswap Papyrus, honeymustard - Freeform
Language: English
Status: Completed
Published: 2018-01-08
Updated: 2018-01-08
Packaged: 2019-03-01 22:42:59
Rating: Explicit
Warnings: Rape/Non-Con
Chapters: 1
Words: 2,255
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/13304883
Author URL: https://archiveofourown.org/users/cardboardhydrates/pseuds/cardboardhydrates
Summary: Stretch has no idea how or why he woke up in Edge's body, but he's going to take advantage of the the chance to act on his feelings for Red, while Red still thinks he's Edge.





	Window of Opportunity

**Author's Note:**

  * For [idontevenknowugh](https://archiveofourown.org/users/idontevenknowugh/gifts).



From the second Papyrus woke up, he knew something was off.

 

Maybe it was the fact that he was actually tucked under the blankets, as if he was the sort of person who actually made his bed. 

 

Or how his body felt foreign to him. 

 

He felt alert in a way he hadn't felt in years, despite having just woken up in the middle of the night. And, as he rubbed his phalanges over his femurs and ribs, he felt scars, loads and loads of tiny scars that he didn't remember having, all over his body. The types of scars you gain in battle.

 

Papyrus made it a point to never get hit in battle.

 

He jumped out of the bed, darting around the room until he found a mirror and stared at the reflection.

 

That wasn't his face. That wasn't his body.

 

He immediately recognized it. It was that weird alternate version of himself they had nicknamed Edge. The two of them were so different, it seemed impossible that they were the same person, but somehow they were.

 

His brother Red, wasn't anything like Papyrus' own brother either. So much so, Papyrus didn't even register him as a brother. He was cool, in a way that was completely different from how Sans was. He was funny, in an awful, bleak sort of way.

 

He was also a completely fucking tease. Always making these sexual jokes, when Papyrus couldn't have him. It was infuriating!

 

Like he knew that Papyrus would love to mess around with him and was taunting him with what he couldn't have. Everyone knew that he and Edge had some fucked up thing going on between them and there was no room for anyone one else between them. 

 

....But now he WAS Edge. As far as Red knew. What other opportunity would he get like this? He could fuck Red, just once, just to get him out of his system, and go back to how things once were, without Red ever knowing.

 

Papyrus quietly snuck out of his double's room and slowly opened the door to Red's room and peeked in. 

 

Red was fast asleep, loudly snoring away. Papyrus slid into the room and carefully closed the door behind him, Soul pounding. Red didn't stir.

 

Why was he so worried about Red waking up? They probably did stuff like this all the time, kinky bastards. Red wouldn't think anything was strange unless Papyrus acted suspiciously. He just had to act just like Edge. Confident and self assured. He strode over to the bed and sat down, staring down at Red.

 

It really wasn't fair. 

 

Edge didn't deserve someone like Red. He was a jerk, and was rude, and he was an idiot. 

 

Meanwhile, Papyrus was nothing but nice to Red, but he got nothing out of it but merciless teasing instead.

 

He deserved to have this. 

 

Still, he hesitated. 

 

If he got caught, it would ruin everything. Their new friends would consider him an outcast, his brother's belief in him would surely be shattered, his easy friendship with Red most of all, forever ruined. He would be a criminal, of the most heinous kind, a reputation he would never get past.

 

If he even lived to see another day. If Red didn't kill him, Edge would.

 

And Red knew Edge better than anyone else.  

 

But what are the odds that he would guess that they had swapped bodies? It sounded completely insane. Besides, it was the middle of the night. Red would probably be too tired to notice anything really strange anyways.

 

He might even think the whole thing was a dream.

 

"Are you just going to sit there and stare at me asshole," Red suddenly mumbled. "Wassup?" Papyrus jumped,  not realizing that Red had woken up. 

 

"It is none of your concern R-Sans," Papyrus scoffed, cursing himself for the near slip. 

 

"Are you sure?" Red asked, "Because you seem kind of jumpy. Did you have a bad dream or something bro?"

 

...fuck it. He's already here, he might as well go with it.

 

Papyrus ground against Red, and grinned. "Not a BAD dream, no." Red groaned, loud, as if the simple touch was almost unbearable. "Fuck, you mean it? Its been ages, I was starting t-to think you'd never be up for this again."

 

God, listening to Red groan like that was ecstasy. He rubbed harder against Red, drinking in the noises he made, and it wasn't long before he saw the soft orange-

 

Oh no.

 

"Sans! Let's....spice things up a little. Make it a little more exciting! Right? Right!" Papyrus wrapped Edge's scarf around Red's eyes.

 

"Um. Okay?? If you want?"

 

Dammit, he was planning on tying Red's to the bed frame, but there was none. Growling, he summoned two bones and flung them at the wall, right above Red's head. 

 

"Has anyone ever told you that you need an actual bed?" He grumbled at Red. 

 

Red laughed, a little shaky. "I might have heard something like that before, yeah."

 

Papyrus unbuckled his belt, and wrapped the belt around Red's arms, directing them to the bones over Red's head.  

 

"....Are you sure about this, Papyrus?" Red asked, "After what happened last time, you didn't seem to want to try this again."

 

....What happened last time? Clearly Red and Edge weren't having wild kinky sex in their sex dungeon every night like he had imagined. Red seemed worried about Edge, and confused about why he was doing this…Was he getting suspicious?

 

"J-just shut up Sans, and quit asking such stupid questions! Of course I'm sure!" He threaded the belt through the hollow space between his bones, assured that he wouldn't be able to slip out, and tied him to the bones jutting out of the wall over his head.

 

Red huffed, “All right, all right, you’re the boss and all that. Just, make sure to use the safe word the moment you’re uncomfortable. Even though his eyes were covered, his face was turned right towards Papyrus. The expression on his face was dead serious. “…And I promise I will.”

 

“Right, right.”

 

At long last, Papyrus pulled out his cock. He stroked himself, imagining how it will feel like once he’s finally inside Red. “I bet you can’t wait to feel this inside you, can you?” He sneered. “You’re desperate for it.”

 

“F-fuck yeah I am,” Red gasped. “It’s been way, way, way too long, come on…”

 

He probably should prepare Red first. Papyrus contemplated the notion of releasing Red’s arms and having him prepare himself, imagining Red fingering himself, begging Papyrus to fill him up…but decided it wasn’t worth the risk of Red getting free, just to save himself the trouble of having to prepare him himself.

He stuck one phalange inside Red’s opening, exploring new territory he had only ever dreamed of. It was warm, almost unbearably so, and soft.

 

Papyrus thrust his finger in a few more times, and added in another.

 

Red winced. “Shit bro, you in a hurry or something?”

 

“Don’t mock me Sans, I know what I’m doing!” Papyrus yelled, face flushing. “You were just begging me to hurry up and fuck you seconds ago!”  

 

“I know but-ugh, can you just give me a minute to adjust? Or two? Or several? Somebody just woke me up in the middle of the night after all.”

 

“Fine.” He almost considered just leaving his fingers there, without moving, but his dick was so hard it was painful, and all he wanted to do was get on with this. So he slowed down just enough to keep Red happy, but continued fingering him at a fairly rapid state.

 

Finally, he seemed loose enough. Papyrus grabbed his dick, lined himself up with Red’s opening, and pressed inside.

 

Holy shit it was TIGHT.

 

“FUCK!” Red yelped, “What the fuck, ow, ow, ow!”

 

Holy shit it felt GOOD.

 

“Oh shut up, you know you love it, you masochist!” Papyrus growled, thrusting deeper into Red, relishing in the feeling of him, his tight muscles squeezing his dick. It felt better than anything he had ever imagined, and with each thrust, as he got deeper inside him, it felt even better.

 

“Wait, bro, hold on, shit-” Red stammered, his words soon faltering into a whimpering mess. Papyrus grinned as Red started to lose coherency, and fucked him harder. 

 

It wasn’t long before Papyrus felt himself approaching his climax. He pounded into Red, so close, desperate to finally finish.

 

As Papyrus climaxed, he breathlessly gasped, “Oh god, you’re amazing Red. Oh my god, that was incredible!”

 

“…What did you call me?”

 

Papyrus stopped breathing. Shit, shit, shit, he just ruined everything!

 

He laughed nervously. “O-oh! I must have gotten used to the others calling you that and said in on accident.”

 

“Oh, so you accidentally called me something besides the name you’ve called me since you were born?” Red demanded. “God, I’m so stupid! I knew something was weird this whole time, but I let it slide because-Who the hell are you, and what the fuck did you do with my brother??”

 

“Don’t be stupid Sans, I’m your brother! Who else could I be?”

 

“Well if you know me as Red, you have to be a Papyrus from a different universe. I don’t think the Classic version would do something like this, so… Stretch?”

 

“…”

 

“…Fuck. I thought we were friends Stretch. Why the fuck would you do that?”

 

…Maybe he could still salvage this.

 

“Look Sans, you’re talking nonsense! All you’re basing this foolish hypothesis off of is me referring to you by a nickname that others refer to you as!” Papyrus insisted. “How about you just go back to sleep and  forget this ridiculous notion?”

 

“…take off the blindfold and prove it to me then.”

 

Papyrus sighed. “Just don’t bite me or anything.” He reached forward, as close as he dared, and pulled off the blindfold as quickly as possible.

 

“Look, don’t you recognize your own brother’s body?” He turned in place, allowing Red to see the scars that littered his body. “And even if I was some other Papyrus masquerading as your brother, could I replicate all these scars? In places I’ve never seen? How could anyone perform such a charade?” 

 

Red stared at him intently, his eyes searching every nook and cranny, as though they had memorized every inch of his brother and he was searching for a flaw, some detail that would give Papyrus away.

 

He would find none. This really was Edge’s body after all. 

 

Finally he looked away and sighed. “All right, I guess it really is you. Sorry I doubted you.” He grinned at Papyrus. “But you know, I’m not all that tired. You up for round two?” He pressed his foot against Papyrus’ pelvis, rubbing against it, until-

 

The room filled with a soft orange light. Papyrus looked away, unable to deny it any longer. He could see Red trembling with rage from the corner of his eye.

“You disgusting sack of shit!” Red shrieked. “Why the fuck are you in my brother’s body? And WHERE THE FUCK IS MY BROTHER?”

 

Who knows?

 

Papyrus just smiled and shrugged nonchalantly. God he wished he had a cigarette right now. 

 

“God I’m going to fucking-” Red stopped, realizing that his arms were still restrained to the bones. “You planned for this.” He struggled in the restraints, trying to break free. “Fuck, I can’t teleport if I’m tied to something else! But of course you already knew that!”

 

“Well, yeah-” Papyrus almost didn’t see the row of bones that Red quietly summoned, but he immediately summoned his own and knocked them out, turned Red’s soul blue, and hissed, “You try that again, and I will destroy your brother’s body. I’ll just go back to my own body, but Edge will be shit out of luck. Just some lost soul without a body, stuck in the void forever.” Red shivered. “Is that what you want to happen to your brother, or are you going to play nicely?”

 

Red didn’t say anything, but he didn’t try to escape, and Papyrus released his hold on him. 

 

“What the hell are you planning on doing with me Stretch?” Red asked. “Are you going to keep me locked up in here and just fuck me all day? People are going to wonder where I am. There’s no way you’ll get away with this.”

 

Papyrus didn’t even know how long this was even going to last. He might wake up in his own body the next morning, he might find himself in Edge’s body for the rest of this timeline, however many weeks, months, even years that lasted. 

 

All that mattered was that no one outside of Red knew about this.

 

“Look Red, everything’s going to be juuuust fine,” Papyrus draped an arm over Red’s shoulder, “Everything will go back to normal, just like none of this ever happened. Like it was all a dream.”

 

“Don’t you fucking touch me like we’re friends you sick rapist fuck.” Red hissed. Papyrus flinched, but moved his arm away.

 

“…All you have to do is not breathe a word of this to anyone. And nothing happens to you, or your brother.” Papyrus stared at Sans, at the fearful, disbelieving look on his face, and took a moment to mourn the friendship the two of them had once had.

 

Well. No point in worrying about the past now. 

 

Papyrus grabbed Sans by the pelvis, roughly rubbing his pubic bone. “Now, what were you saying earlier about round two?”

**Author's Note:**

> Hey Uggy! I'm so sorry this is so late, but here it is! I was really excited to be your secret santa, you were one of the people who inspired me to make my account and start writing AUs, and I really wanted to write something that felt like something you might like! I really hope its up to your standards!


End file.
